Mitosis Meiosis

Question 1

Phases of Mitosis: Prophase

Answer 1

chromosome condensation, centrosome separation

Question 2

Phases of Mitosis: Prometaphase

Answer 2

nuclear envelope breakdown

Question 3

Phases of Mitosis: Metaphase

Answer 3

chromosome alignment

Question 4

Phases of Mitosis: Anaphase

Answer 4

sister chromatid separation and segregation

Question 5

Phases of Mitosis: Telophase

Answer 5

cytokinesis

Question 6

What type of filament is most important in prometaphase, metaphase and anaphase?

Answer 6

mircrotubules (astral, polar, kinetochore)

Question 7

What type of filament is most important in telophase?

Answer 7

actin

Question 8

explain the relationship between a chromosome and a chromatid

Answer 8

a chromatid is one copy of a duplicated chromosome as long as it is joined by a centromere with the other copy (sister chromatids), once split in anaphase they are called daughter chromosomes

Question 9

homologous chromosomes

Answer 9

maternal and paternal copies of the same chromosome

Question 10

what protein holds sister chromatids together?

Answer 10

cohesins

Question 11

What are the two important reasons to have sister chromatids bound together in the cell cycle?

Answer 11

1. DNA repair - template for double stranded break repair 2. correct alignment on the mitotic spindle

Question 12

3 functions of the kinetochore

Answer 12

1. attachment site for the microtubules on the chromosome 2. generate force to segregate chromosomes 3. cell cycle checkpoint

Question 13

How many kinetochores does each chromosome have?

Answer 13

2, one per sister chromatid so they can migrate to opposite poles (bi-oriented)

Question 14

What must happen for the sister chromatids to separate in anaphase?

Answer 14

the microtubules must be attached and begin to retract AND proteolysis of the cohesin molecules

Question 15

what coordinates where the plane of cleavage is within the cell during cytokinesis?

Answer 15

astral microtubules designate the position of the cleavage furrow (important when asymmetric division in necessary)

Question 16

What is a common error in chromosome segregation and what is ther result?

Answer 16

one kinetochore binds microtubules of both spindle poles - can result in aneuploid karyotypes

Question 17

How is meiosis different than mitosis?

Answer 17

Meiosis is one round of replication followed by two rounds of division (mitosis is one replication: one division)

Question 18

What happens to the number of chromosomes in meiosis?

Answer 18

diploid –> haploid (each gamete has one homologous chromosome)

Question 19

What is the hallmark of Meiosis

Answer 19

Homologous Recombination between homologous chromosomes (not sister chromatids)

Question 20

Why is homolgous recombination necessary for correct meiotic division?

Answer 20

in the first round of meiosis, the homologous chromosomes line up together and separate, the only thing that keeps the homologous chromosomes together are the cohesin molecules where the cross over has occurred

Question 21

What is the purpose of the synaptonemal complex?

Answer 21

it is a structure that suppresses recombination between sister chromatids to promote strand exchange between homologous chromosomes in meiosis

Question 22

What happens in the first meiotic division?

Answer 22

homologous chromosomes are separated by proteolysis of cohesin between sister chromatid arms, cohesion between sister chromatid centromeres is retained (reductional division)

Question 23

What happens in the second meiotic division?

Answer 23

sister chromatids separate by proteolysis of cohesion between centromeres (equational division)

Question 24

What is the normal human karyotype?

Answer 24

46, XY

Question 25

What is a current theory for why chromosome missegregation is more common with increased maternal age?

Answer 25

deterioration of sister chromatid cohesion over time (oocye formed in fetal development, cohesion has to last until conception 20-30-40 yrs later)

Question 26

SUMMARY CARD: differences between mitosis and meiosis

Answer 26

1. homologous chromosomes pair in meiosis 2. recombination only in meiosis 3. in meiosis one in females, prophase is extended 4. meosis has 2 rounds of division per DNA replication event 5. two steps of cohesion release in meiosis 6. sister chromatid kinetochores behave as one in meiosis 1 7. incomplete cytokinesis and asymmetric spindle position can happen in meiosis (oogenesis and spermatogenesis)